1. Field of the Invention
The invention relates to amorphous metal alloy compositions, and, in particular, to amorphous alloys containing iron, nickel, cobalt and/or chromium having improved resistance to embrittlement upon heat treatment.
2. Description of the Prior Art
Investigations have demonstrated that it is possible to obtain solid amorphous metals for certain alloy compositions. An amorphous substance generally characterizes a non-crystalline or glassy substance, that is, a substance substantially lacking any long range order. In distinguishing an amorphous substance from a crystalline substance, X-ray diffraction measurements are generally suitably employed. Additionally, transmission electron micrography and electron diffraction can be used to distinguish between the amorphous and the crystalline state.
An amorphous metal produces an X-ray diffraction profile in which intensity varies slowly with diffraction angle. Such a profile is qualitatively similar to the diffraction profile of a liquid or ordinary window glass. On the other hand, a crystalline metal produces a diffraction profile in which intensity varies rapidly with diffraction angle.
These amorphous metals exist in a metastable state. Upon heating to a sufficiently high temperature, they crystallize with evolution of a heat of crystallization, and the X-ray diffraction profile changes from one having glassy or amorphous characteristics to one having crystalline characteristics.
It is possible to produce a metal which is totally amorphous or which comprises a two-phase mixture of the amorphous and crystalline state. The term "amorphous metal", as employed herein, refers to a metal which is at least 50% amorphous, and preferably 80% amorphous, but which may have some fraction of the material present as included crystallites.
Proper processing will produce a metal alloy in the amorphous state. One typical procedure is to cause molten alloy to be spread thinly in contact with a solid metal substrate such as copper or aluminum so that the molten alloy loses its heat to the substrate. When the molten alloy is spread to a thickness at about 0.002 inch, cooling rates of the order of 10.sup.6 .degree. C/sec are achieved. See, for example, R. C. Ruhl, Vol. 1, Materials Science and Engineering, pp. 313-319 (1967), which discusses the dependence of cooling rates upon the conditions of processing the molten alloys. Any process which provides a suitable high cooling rate, as on the order of 10.sup.5 .degree. to 10.sup.6 .degree. C/sec, can be used. Illustrative examples of procedures which can be used to make the amorphous metals are the rotating double roll procedure described by H. S. Chen and C. E. Miller in Vol. 41, Review of Scientific Instruments, pp. 1237-1238 (1970) and the rotating cylinder technique described by R. Pond, Jr. and R. Maddin in Vol. 245, Transactions of the Metallurgical Society, AIME, pp. 2475-2476 (1969).
Novel amorphous metal alloys have been disclosed and claimed by H. S. Chen and D. E. Polk in U.S. Pat. No. 3,856,513, issued Dec. 24, 1974. These amorphous alloys have the formula M.sub.a Y.sub.b Z.sub.c, where M is at least one metal selected from the group consisting of iron, nickel, cobalt, chromium and vanadium, Y is at least one element selected from the group consisting of phosphorus, boron and carbon, Z is at least one element selected from the group consisting of aluminum, antimony, beryllium, germanium, indium, tin and silicon, a ranges from about 60 to 90 atom percent, b ranges from about 10 to 30 atom percent and c ranges from about 0.1 to 15 atom percent. These alloys have been found suitable for a wide variety of applications, including ribbon, sheet, wire, powder, etc. Amorphous alloys are also disclosed and claimed having the formula T.sub.i X.sub.j where T is at least one transition metal, X is at least one element selected from the group consisting of aluminum, antimony, beryllium, boron, germanium, carbon, indium, phosphorus, silicon and tin, i ranges from about 70 to 87 atom percent and j ranges from about 13 to 30 atom percent. These alloys have been found suitable for wire applications.
Ductility is generally desirable either to render mechanical applictions possible or to ease the handling and processing of the product. It is known that amorphous metal alloys tend to lose ductility in bending upon heating to temperatures near which the onset of crystallization occurs (crystallization temperature). Often, prolonged heating at lower temperatures is sufficient to induce embrittlement. Many of the amorphous alloys containing iron, nickel, cobalt and/or chromium known in the art, which include phosphorus as an aid to glass formation tend to embrittle upon heating in the temperature range of about 200.degree. to 350.degree. C. While many applications involving these amorphous alloys would not require such heat treatment, there are specific instances where such heating would be necessary and where it would be desirable to utilize these alloys, many of which are relatively inexpensive compositions.